Treatment of sulphite-wood-pulp liquor



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R, OT TURK HAVEN, PENNSYLVANIA.

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The process includes a number of which are enumerated and explainedbelow. The first step consists of the collection of the sulphite wasteliquors from the blow pits it into whichthe sulphite pulp is dischargedfrom the digesters. The liquor is drained from the pulp through aperforated bottom in the blow pits. llf necessary or justified under theparticular conditions most of the tilt liquor which may still cling tothe fibrous pulp after draina e by virtue of capillarity may bedisplaced by the gradual addition of water, which is evenly distributedover the surface of the pulp mass.

Tn the second step these liquors while still hot are subjected tofiltration through a filter capable of retaining any and allfibers andsolids in suspension. These fibers are returned to the blow pit, and theclear liquor an while still hot may or may not be sprayed through anozzle pr nozzles into the atmosphere, according .to the process whichthe liquors are subjected to for the recovery of organic constituents.at The third step in the process consists in the collection of these(sprayed or unsprayed) liquors, and subsequent treatment at atemperature of substantially not less than 80 to fi5 ce ntigrade, withthe oxide or hydroxide to of an alkaline earth metal in a tank providedwith an elficient agitator, until the loosely combined sulphur dioxidecontained in the liquoris changed to the sulphite of the alkaa lineearth metal, and until the hydrogen ion as concentration of the liquoris substantially suchas is designated by the symbol or expression plilfi. The first half or two-thirds (not more) ofthe required treatment maybe done in' soine respectsadvantageously with to the equivalentamount'of a carbonate of an alkalineeai'th metal, if this is desirableor cheaper, but the rate-of reaction is afiected unfavorably, thecarbonate of an alkaline steps,

earth metal being considered an equivalent at and as such'included inthe claims. When \using the oxide, it is always slaked, forming ahydroxide solution or suspension. The hydroxideis always furnished tothe liquor in dissolved or suspended form. an The selection of thealkaline earth metal oxide, hydroxide, or carbonate is governed by costto a large. extent,-but disregarding this factor, or weighing it againstthe effectiveness of the result, the chemicalconsiderations enteringinto the proposition are the solubilities of the treating compounds, and

application filled f ebruary tit, that. serial No. twat-ti.

the solubilities of the products resulting therefrom. Tn this process itis most favortlti ing order, viz., barium, strontium, calcium,

and magnesium. The comparatively low cost of lime, and the relativeinsolubility of its sulphate and sulphite make it quite satis factoryfor the manufacture of a suitable product at the present time. Tn stepthree one object is to accomplish. principally three things, (1) theremoval by conversion into insoluble form of some of the sulphurpresent, whether it be in the form of sulphites, sulphates, sulphurousacid gas, or loosely combined and reversible sulphurous acid, (2) thechange of the reaction of the liquor from acidic to basic, (3) theconversion into insoluble form of any such compounds which would takeplace at much slower rate at lower temperature. lit may be noted thatthe reagent used-should contain only minimum amounts of iron.

The fourth step in the process consists in filtering the insolublematter produced in the third step from the resulting liquor. Gompleteseparation is desirable, and the separated liquor should preferably becrystal clear. if or this reason it is advisable to subject the liquorto sedimentation in any of the known forms of sedimentation orthickening apparatus, or simply 111 a tank, for a sufficient time tosettle the major portion of the larger particles. The supernatant liquoris drawn ofi and passed through a-filter capable of holding the finestprecipitates. While ll do not limit this procedure to any particular aform of filtration apparatus, it will be found preferable in most casestouse a high speed centrifugal of the unperforated basket or bowl. type,which discharges the clear liquid from the basket or bowl through thecake, which is precipitated in a compact mass on the side of the' bowlorbasket, while the filtrate flows over the top of the basket or bowl, orout of the bottom. Tn step four some of the purposes are the minimizingof the decomposition of the liquor in its subsequent treatment fororganic products recovery, the minimizing of corrosion of and depositionof scale on the surfaces of ltd without passing it llltl anyconcentration apparatus in which the liquor is subsequently treated, andthe production of a purer resulting concentrated product than iffiltration were not resorted to, but one of the principal reasons forfiltration is the recovery of these mineral solids, which it is thepurpose of the invention to utilize in the preparation of the sulphitecooking liquor used in the beginning of the sulphite pulp manufacturingprocess, because of the alkaline earth metals and the sulphur thesesolids contain.

The fifth step covers the proper utilization of the above separatedsolids by adding them to sulphite cooking liquor in the course of itspreparation. The chemical considerations involved are as follows:Regardless of the alkaline earth compound selected for the treatment inthe th1rd step, the residue, or

at least the major portion of it, is soluble in sulphite liquorcontaining excess sulphurous acid, that is, in the cooking liquor oracid used in sulphite pulp manufacture. The sediment will contain moresulphite and less hydroxide if the alkaline earth metal compounds arechosen in the order named, i. e., progressing from barium to magnesium.Both the sulphite and the hydrate are valuable in the making of thecooking liquor, as by adding the sulphite tothe liquor in the course ofmanufacture the soluble bisulphites are formed, and the equivalentamount of sulphur and alkaline earth metal base is saved over that usedin the original preparation of the liquor. The hydroxide part of thesediment is valuable because these compounds unite with the sulphurdioxide gas used in the preparation of the cooking acid, forming thecorresponding bisulphite compounds, effecting an equivalent saving inthe alkaline earth base, usually limestone or lime, used in the cookingliquor preparation. These 'reactions may be expressed symbolically asfollows In the above equation m and n are arbitrary numbers and R-is themetal.

In practicing this step the sediment is con-- veyed by suspension inwater, or any other method of conveyance to a tank, where it may bemixed with sulphite cookin liquor containing a considerable excess ofree sulphurous acid, or may be treated along with the cooking liquorwiththe highly concentrated relief gas coming from the digesters. Thetank maybe so constructed and arranged that the whole massis subjectedto a mild stirring action. The tank may also be arranged that a mildpressure may be carried, to facilitate the reaction. The sulphurous acidpresent dissolves nearly all of the sediment, the insoluble matterremaining'being of little or no value to the process.

The tank is also provided with a means of filtration or sedimentation,preferably the latter, so that these undesirable insoluble solids willnot be carried along through the subsequent steps of the sulphitecooking liquor making process, The liquor, after sedimentation, isdischarged from the tank ready for further use in the sulphite cookingprocess.

It is also to be noted that when barium or strontium is used, thoughonly in amounts equivalent to a relatively small proportion of the totaltreating agent, an additional advantage is realized in that thesulphuric acid present in the cooking acid is precipitated as the verysparingly soluble sulphate, resulting in the removal of this acid fromthe sphere of action in the sulphite pulp cooking process. Thissulphuric acid, while ordinarily conceived to be present in the combinedform with lime (calcium sulphate) in the cooking liquors, acts as if inthe free state, and in fact may partially exist in the free state,because of the effect of the far greater relative mass of freesulphurous acid present. In other words, in the cooking the sulphuricacid can at least in part come into play according to the followingformula:

This sulphuric acid, at the high temperature at which it exists, exertsa hydrolytic action on the pulp in the sulphite (ligcstel,

tending to weaken and soften it, and decrease the yield of the fiber. Ithas been the experience in thepast that a better pul was always obtainedwhen sulphuric aci was present only in the smallest amounts possible.

The above procedure therefore clearly effects a considerable economy inthe operation, and also offers some advantage in the improvement of themethod of preparing the sulphite cooking liquors.

It is understood that the sulphite waste liquor which remained after thefiltration in the fourth step, is to be further concentrated. orotherwise treated, and thereby converted into useful products, such asbinders, adhesives, tanning extracts, etc., by any of the knownprocesses, and it is furthermore understood that it is particularlyadapted to the manufacture of a tanning extract by the rocreaaoocontaining principally sulphites insoluble in water by neutralizing thewaste liquor with alkaline earth metal base suflicient to produce thedegree of alkalinity expressed as pH=9 or greater alkalinity andsu'llicient to decompose the reversibly combined sulphurous acid presentin combinationwith the substances dissolved from the wood to increasethe recovery of the sulphur as monosulphite, and in the preparation ofcooking liquor, treating the solids with cooking acid which containsfree sulphurous acid for the conversion of the solids into solublebisulphites.

' 2. ln the treatment of wood pulp liquor the process which consists inrecovering from the sulphite waste liquor solids containing principallysulphites insoluble in water y neutralizing the waste liquor withalkaline earth metal base sufficient .to producethe degree of alkalinityexpressed as pl-l[=9 or greater alkalinity and suflicient to decomposethe reversibly combined sulphurous acid present in combination with thesubstances dissolved from the wood to increase the re covery of thesulphur as monosulphite.

3; In the treatment of wood pulp liquor the process which consists inrecovering from the sulphite waste liquor solids useful in thepreparation of sulphite cooking liquor and including sulph-itesinsoluble in water by neutralizing the waste liquor at substantially theprocess which consists in recovering from.

the sulphite waste liquor solids lncludmg sulnot less than 80 to 85 C.with alkaline earth metal base until the hydrogen ion concentration ofthe liquor is pH=9, or greater alkalinity and in the manufacture ofcooking liquor treating the solids with sulphurous acid present in thecooking liquor for the conversion of the solids into solublebisu'lphite.-

4:. ln the treatment of wood pulp liquor phites insoluble in water byneutralizing the waste liquor at substantially not less than 80 to 85 Q.with alkaline earth metal base until the hydrogenion concentration ofthe liquor is pH=9 or greater alkalinity.

5.111 the treatment of wood pulp liquor the process which consists inrecovering from the sulphite waste liquor solids useful in thepreparation of sulphite cooking liquor and including insoluble sulphitesby neutralizing the Waste liquor until the hydrogen ion concentration ofthe liquor is pH=9 or greater alkalinity and decomposing the reversiblesulphurous acid present in combination with the substances dissolvedfrom the wood to increase the recovery of the sulphur as monosulphite atsubstantially not less than 80 to 85 C.'with alkaline earth metalcompounds including some barium or strontium having basic deportmenttoward acid solutions and in the manufacture of the cooking liquortreating the solids with sulphurous acid present in the cooking liquorfor the conversion of the solids into soluble bisulphites.

6. In the treatment ofwood pulp liquor the process which consists inrecovering from the sulphite waste liquor solids including insolublesulphites by neutralizing the waste liquor until the hydrogen ionconcentration of the liquor is pH==9 or greater alkalinity anddecomposing the reversible sulphurous acid present in combination withthe substances dissolved from the wood to increase the re coverysubstantially not less-than to C. with alkaline earth metal compoundshaving basic deportment toward acid solutions.

7. In the treatment of sulphite wood pulp liquor the process whichconsists in recov- .ering from the waste liquor solids useful in presentin the cooking liquor to convert them into soluble bisulphites whichreacting with the free sulphuric acid in the cooking liquor eliminatesuch acid therefrom.

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of the sulphur as monosulphite at

